1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus.
2. Description of the Related Art
An electrophotographic image forming apparatus forms an electrostatic latent image on a photosensitive member by scanning the photosensitive member using laser light deflected by a rotating polygonal mirror, and forms an image by developing the electrostatic latent image using toner. The density of the image changes by changing the light amount of the laser light. Lenses and mirrors are arranged on an optical path from the rotating polygonal mirror to the photosensitive member. Along the scanning direction of the laser light deflected by the rotating polygonal mirror, the laser light deflected by the rotating polygonal mirror is incident on various positions of the lenses and mirrors depending on the rotation angle of the rotating polygonal mirror. The transmittance of the lenses through which the laser light passes and the reflectance of the mirrors that reflect the laser light are uneven along the scanning direction. Therefore, along the scanning direction of the laser light, the light amount (intensity) of the laser light varies among different positions on the photosensitive member irradiated by the laser light (scanning positions). This gives rise to the problem that the density of the image is uneven along the scanning direction of the laser light.
Japanese Patent Laid-Open No. 2005-178041 proposes an image forming apparatus that executes shading control in accordance with scanning positions without using a digital-to-analog converter.
However, the invention of Japanese Patent Laid-Open No. 2005-178041 does not take into account changes in the light emitting characteristics of the laser light caused by the ambient temperature around the image forming apparatus and temporal changes in the image forming apparatus. Therefore, according to this invention, the degree of control on the light amount deviates from the degree of control set for initial adjustment, thus giving rise to error in the degree of control.